1. Field of the Invention:
The present invention relates to a plant for manufacturing cement clinker.
2. Description of the Related Art:
A typical conventional plant or apparatus for manufacturing cement clinker incorporates a combination of a fluidized-bed type sintering furnace, a cooling system, an air-preheater, a heat-exchanging cyclone and a dust collector. This conventional apparatus essentially requires the use of nuclide clinker. The nuclide clinker is typically fine particles of clinker and is circulated through a nuclide clinker circulating line. This apparatus, however, suffers from disadvantages such as a large heat loss due to circulation of the nuclide clinker and inefficient recovery of the sensible heat possessed by the burned clinker, resulting in a low thermal efficiency and difficulty in the reduction of fuel consumption.
In order to overcome these problems of the prior art, the present inventors have already proposed, as in Japanese Pat. Publication No. 13738/1985, an apparatus for producing cement clinker without necessitating the use of nuclide clinker. This apparatus includes a suspension preheater composed of a plurality of cyclones, a spouted-bed granulating furnace, a fluidized-bed type sintering furnace, a cooling apparatus and so forth, wherein the lower portion of the spouted-bed type granulating furnace and the upper portion of the fluidized-bed type sintering furnace are connected to each other through a waste-gas duct. More specifically, this apparatus is characterized in that the preheated material from the suspension preheater is charged into the duct which interconnects the cooling system and the spouted-bed type granulating furnace, so that the material is mixed with the hot cooling air extracted from the cooling system while exchanging heat therebetween, the mixture being then fed to the spouted-bed type granulating furnace. With this arrangement, it is possible to eliminate the problem that the molten component of the material adheres to and grows on the inner surface of the duct interconnecting the cooling system and the granulating furnace so as to coat the inner surface of the duct. In addition, it is possible to make an efficient use of the heat collected from the cement clinker cooling system.
In operation of the apparatus disclosed in Japanese Unexamined Pat. Publication No. 13738/1985, the atmosphere in the spouted-bed type granulating furnace is maintained at a liquid-phase generating temperature which generally ranges between 1250.degree. and 1350.degree. C. Partly because the burner of the spouted-bed type granulating furnace in this apparatus is provided on the straight barrel wall of the furnace, and partly because the air suspending the material to be calcined is introduced such as to cover the region near the inner surface of the wall of the granulating furnace, the fuel supplied from the burner does not form any local hot region which would exhibit a temperature much higher than the temperature in the peripheral region. In consequence, a substantially uniform temperature distribution is realized in the spouted bed. The substantially uniform temperature distribution, i.e., lack of a hot local region, inevitably reduces the amount of liquid phase which is formed by melting of the cement material powder. In consequence, the granules formed in the granulating furnace tend to have too small and non-uniform sizes, and the granulation takes place only at a small rate. The generation of the liquid phase would be increased by rising the temperature of the spouted bed. However, in this known apparatus, the bed temperature rises uniformly so that the stability of the spouted bed tends to be impaired due to agglomeration in the bed.